This invention is generally directed to a process, and more specifically to a process for achieving a reduction in the energy requirements for affecting flash fusing in an electrostatographic imaging process. Therefore, in accordance with the present invention there is provided a process for permanently fixing developed images to a supporting substrate with less energy by, for example, forming a waxy interface between the toner composition and the substrate. In one embodiment of the present invention, developed images are permanently fixed to a paper substrate by flash fusing with an energy reduction of from about 5 to about 20 percent, and wherein there is situated between the toner composition and the paper substrate a waxy layer. The process of the present invention is particularly useful in electrostatographic imaging apparatuses having incorporated therein a flash fusing device such as a xenon lamp.
The formation and development of images on the surface of electrophotographic materials, referred to in the art as photoreceptors for example by electrostatic means, is well known, these processes involving subjecting the photoconductive material to a uniform charge; and subsequently exposing the surface thereof to a light image of the original to be reproduced. The latent image formed on the xerographic photoconductive surface is developed with toner particles specifically prepared for this purpose. Thereafter, the developed image can be transferred to a final support material such as paper, and affixed thereto to obtain a permanent record or copy of the original. Numerous method are known for applying the electrostatic toner particles to the electrostatic latent image, including for example, cascade development, magnetic brush development, powder cloud development and touchdown development.
The image formed can be fixed by a number of various well known techniques including, for example, vapor fixing, heat fixing, pressure fixing, or combinations thereof, as described for example in U.S. Pat. No. 3,539,161. These techniques of fixing, while suitable for certain purposes, suffer from some deficiencies thereby rendering their use either impractical or difficult for specific electrostatographic applications. For example, it is difficult to construct an entirely satisfactory heat fuser which has high efficiency, can be easily controlled, and has a desirable short warm-up time. Also, heat fusers sometimes burn or scorch the support material. Somewhat similar problems including, for example, image offsetting and undesirable resolution degradation, are present with pressure fusing methods. Additionally, with these processes consistently desirable permanent images are not obtained. Further, although vapor fixing has advantages, one of its main disadvantages is that a toxic solvent is used, therefore, in many situations this method becomes commercially unattractive because of health hazards associated therewith. Also, equipment and apparatus to sufficiently isolate the fuser in vapor processes from the surrounding area is very complex, costly and difficult to operate.
Many of the modern electrostatographic reproducing apparatuses, which are capable of producing copies at an extremely rapid rate, created the need for the development of new materials and processing techniques. With these systems, radiant flash fusing is one of the preferred fixing processes selected in that the energy which is emitted in the form of electromagnetic waves is immediately available and requires no intervening medium for its propogation. Although an extremely rapid transfer of energy between the source and the receiving body is provided with the flash fusing process, a problem encountered with this process resides in obtaining an apparatus which can fully and efficiently utilize a preponderance of the radiant energy emitted by the source during a relatively short flash. The toner image in these systems usually comprises a relatively small percentage of the total area of the copy receiving the radiant energy causing most of the energy generated to be wasted as it is transmitted to the image, or is reflected away from the fusing areas. Furthermore, many of the toner compositions currently available, particularly colored toner compositions, contain pigments which do not absorb energy in the near infrared region of the spectrum thereby necessitating the supply of larger amounts of energy to these compositions to affect fusing. Moreover, many of the known colored toner compositions contain pigments therein which do not absorb energy in the near infrared and/or ultraviolet region of the spectrum, thus only about 33 percent of the spectral energy generated, for example, from presently used Xenon lamps is desirably absorbed by the colorants contained in the toner composition.
Specifically, for example, radiation energy emitted from a Xenon flash lamp, or similar source, is absorbed by the pigment or dye contained in the toner composition; and thereafter, this energy is converted to thermal energy by a radiationless decay process enabling heat generation causing the particles to fuse. The flash energy used is absorbed in a layer of toner of finite thickness adjoining the outer toner surface with absorption being greatest at the surface. This energy is also constantly decreasing with increasing distance from the outer toner surface. The flash generated is of very short duration, on the order of about one millisecond; and consequently, the toner regions very close to the surface are heated to a much higher temperature than the toner mass as a whole.
Examples of known flash fusion systems that may be selected for the present invention include those as described in U.S. Pat. Nos. 3,529,125; 3,903,394; and 3,474,223; the disclosure of each of these patents being totally incorporated herein by reference. Generally, the flash fuser selected contains a Xenon lamp, the output of the lamp being primarily in the visible and near infrared wavelengths of the regions. The output of the flash lamp is measured by Joules using the capacitor bank energy in accordance with the formula 1/2 CV.sup.2 wherein C is capacitance and V is the voltage. One of the main advantages of such a flash fuser over other known methods of fusing is, as indicated herein, that the energy propagated in the form of electromagnetic waves is immediately available, and no intervening source is needed. Also, such flash fusing systems do not require long warm-up periods, and the energy does not have to be transferred through a relatively low conductive or corrective heat transfer mechanism.
Moreover, toner and developer compositions with waxy materials are known. Thus, for example, there is described in British Patent No. 1,442,835 a toner composition comprised of a styrene homopolymer or copolymer resin, and at least one polyalkylene compound selected from polyethylene and polypropylene. According to the disclosure of this patent, reference page 2, beginning at line 90, the starting polymer resin may be either a homopolymer of styrene, or a copolymer of styrene with other unsaturated monomers, specific examples of which are disclosed on page 3, beginning at line 1. Polyalkylene compounds selected for incorporation into the toner compositions disclosed in this patent include those of a low molecular weight, such as polyethylene, and polypropylenes of an average molecular weight of from about 2,000 to about 6,000.
Additionally, there is illustrated in U.S. Pat. No. 4,460,672, the disclosure of which is totally incorporated herein by reference, a developer composition mixture comprised of electrostatic toner particles consisting of resin particles, pigment particles, a waxy material with a molecular weight of from about 500 to about 20,000, and further included in the composition from about 0.5 percent by weight to about 10 percent by weight of a charge enhancing additive selected from, for example, alkyl pyridinium halides, organic sulfonate compositions, and organic sulfate compositions.
Also, there is disclosed in U.S. Pat. No. 4,206,247, the disclosure of which is totally incorporated herein by reference, a developer composition comprised of a mixture of resins including a low molecular weight polyolefin and alkyl modified phenol resins. More specifically, it is indicated in this patent, reference column 4, line 6, that the invention is directed to a process which comprises the steps of developing an image with toner particles containing in certain proportions at least one resin selected from group A; and at least one resin selected from group B, wherein the resins of group A include a low molecular weight polyethylene, a low molecular weight polypropylene, and similar materials; and wherein the group B resins include natural resin modified maleic acid resins, and natural modified pentaerythritol resins. As examples of group A resins, there are mentioned polystyrene, styrene series copolymers, polyesters, epoxy resins, and the like, reference the disclosure in column 5, line 47. The molecular weight of the polypropylene, or polyethylene used is from about 1,000 to about 10,000, and preferably from about 1,000 to about 5,000.
There are also described in various copending applications toner compositions with wax components therein, reference for example U.S. Ser. No. 655,381 now U.S. Pat. No. 4,556,624, entitled Toner Compositions with Crosslinked Resins and Low Molecular Weight Wax Components, the disclosure of which is totally incorporated herein by reference. Specifically, the aforementioned copending application illustrates an improved positively charged electrostatic toner composition comprised of a polyblend mixture of a crosslinked copolymer composition; and a second polymer, pigment particles, a wax component of a molecular weight of from about 500 to about 20,000, and a charge enhancing additive. Other patents of interest include U.S. Pat. No. 3,079,342, relating to toners comprised of polystyrene and polymeric modifiers incorporated therein such as long chain thermoplastic plasticizers; U.S. Pat. No. 4,329,415, relating to magnetic developer compositions with waxes therein such as vegetable waxes, whale wax and synthetic waxes including polyethylene wax, and polypropylene wax; U.S. Pat. No. 4,362,803, describing one component magnetic developers with low molecular weight polyethylene and polypropylene; and U.S. Pat. No. 4,385,107, disclosing toner compositions comprised of specific graft copolymers inclusive of polyethylene and polyproplyene.
Nevertheless, there remains a need for processes wherein the energy emitted for the fixing of images is substantially reduced. Also, there is a need for electrostatic processes wherein the developed images are permanently fixed to a supporting substrate with a flash fusing device that emits 5 to 20 percent less energy as compared to prior art fixing processes. Furthermore, there is a need for processes for affecting the permanent fixing of images of high quality to paper substrates wherein the amount of energy needed for flash fusing is from about 4 to about 8 joules/inch.sup.2. Moreover, there is a need for processes wherein a low molecular weight wax component is present as a coating on the exterior surfaces of the toner particles, and wherein less energy is required during the flash fusing process. Also, there is a need for processes that enable a reduction in the flash fusing energy requirements in a xerographic imaging system wherein there is situated between the developed image and the paper substrate a waxy layer.